1. Field of the Invention
The invention relates to a projection display, more particularly a single-lens projection display that utilizes reflective light modulators.
2. Description of the Related Art
In a conventional projection display, an input light beam, which contains red, green and blue color components, is processed before providing the same to a projection lens so as to generate an output image.
Referring to FIG. 1, a conventional single-lens projection display 1 is shown to include a first light polarization selector 11, a second light polarization selector 12, a polarization beam splitter prism 13, a dichroic beam splitter prism 14, a first light modulator 15, a second light modulator 16, a third light modulator 17, a polarizer 18, and a projection lens 19. An input light beam 10, which is a white light beam, is separated into first, second and third color components 101, 102, 103, such as red, green and blue color components, for processing by the first, second and third light modulators 15, 16, 17, respectively.
Each of the first and second light polarization selectors 11, 12, such as the ColorSelect(trademark) filter products available from ColorLink Inc., serves to convert the polarization state of a predetermined color component, without altering the polarization state of the other color components. In the projection display 1 of FIG. 1, the polarization state of the third color component 103, such as the green color component, is changed, whereas the polarization state of the first and second color components 101, 102 remains unaltered, after the color components 101, 102, 103 pass through the first and second light polarization selectors 11, 12.
The polarization beam splitter prism 13 reflects light of a first polarization state, such as S-polarized light, in a transverse direction, and allows light of a second polarization state, such as P-polarized light, to pass therethrough.
The dichroic beam splitter prism 14 is used to separate two different color components. In the projection display 1 of FIG. 1, the dichroic beam splitter prism 14 allows the first color component 101 to pass directly therethrough, and reflects the second color component 102 in a transverse direction, thereby separating the first color component 101 from the second color component 102.
Each of the first, second and third light modulators 15, 16, 17 is a reflective light valve, and is disposed adjacent to one of the dichroic beam splitter prism 14 and the polarization beam splitter prism 13 so as to receive a respective one of the first, second and third color components 101, 102, 103 therefrom. When activated, each of the first, second and third light modulators 15, 16, 17 modulates the respective one of the first, second and third color components 101, 102, 103, and changes the polarization state of the respective one of the first, second and third color components 101, 102, 103. The first, second and third light modulators 15, 16, 17 then reflect modulated first, second and third color components 101, 102, 103 back to the adjacent one of the dichroic beam splitter prism 14 and the polarization beam splitter prism 13.
The polarizer 18 allows light of a predetermined polarization state to pass therethrough, and absorbs light of the other polarization state. In the projection display 1 of FIG. 1, the polarizer 18 allows P-polarized light to pass therethrough, and absorbs S-polarized light.
In operation, when the first light polarization selector 11 receives the S-polarized white input light beam 10, the S-polarization state of the first and second color components 101, 102, such as the red and blue color components, remains unaltered, whereas the S-polarization state of the third color component 103, such as the green color component, is changed to the P-polarization state, after the first, second and third color components 101, 102, 103 pass through the first light polarization selector 11. The polarization beam splitter prism 13 receives the S-polarized first and second color components 101, 102 and the P-polarized third color component 103 from the first light polarization selector 11 at a first side thereof, reflects the S-polarized first and second color components 101, 102 in a transverse direction such that the S-polarized first and second color components 101, 102 pass through a second side thereof, and permits the P-polarized third color component 103 to pass directly through a third side thereof opposite to the first side.
The dichroic beam splitter prism 14, which is disposed adjacent to the second side of the polarization beam splitter prism 13, receives the S-polarized first and second color components 101, 102 therefrom. The first color component 101 passes directly through the dichroic beam splitter prism 14, whereas the second color component 102 is reflected by the dichroic beam splitter prism 14 in a transverse direction.
The first and second light modulators 15, 16 are disposed adjacent to the dichroic beam splitter prism 14 so as to receive the S-polarized first and second color components 101, 102 respectively therefrom. The first and second light modulators 15, 16 modulate the respective one of the first and second color components 101, 102, and change the polarization state of the respective first or second color component 101, 102 from the S-polarization state to the P-polarization state when the first and second light modulators 15, 16 are activated. The first and second light modulators 15, 16 reflect the corresponding modulated color component back to the dichroic beam splitter prism 14 for reception by the polarization beam splitter prism 13.
The third light modulator 17 is disposed adjacent to the third side of the polarization beam splitter prism 13 so as to receive the P-polarized third color component 103 therefrom. The third light modulator 17 modulates the third color component 103, and changes the polarization state of the third color component 103 from the P-polarization state to the S-polarization state when the third light modulator 17 is activated. The third light modulator 17 reflects the modulated S-polarized third color component 103 back to the polarization beam splitter prism 13.
The modulated P-polarized first and second color components 101, 102 from the dichroic beam splitter prism 14 will be allowed by the polarization beam splitter prism 13 to pass directly through a fourth side thereof opposite to the second side for reception by the second light polarization selector 12. The modulated S-polarized third color component 103 from the third light modulator 17 will be reflected by the polarization beam splitter prism 13 in a transverse direction so as to pass through the fourth side thereof for reception by the second light polarization selector 12.
When the second light polarization selector 12 receives the modulated first, second and third color components 101, 102, 103 from the polarization beam splitter prism 13, the polarization state of the modulated P-polarized first and second color components 101, 102 remains unaltered, whereas the polarization state of the modulated S-polarized third color component 103 will be changed to the P-polarization state.
The polarizer 18 permits only pure P-polarized color components to pass therethrough, and absorbs S-polarized color components. The modulated P-polarized first, second and third color components 101, 102, 103 from the polarizer 18 are recombined as they pass through the projection lens 19 for projecting a color image on a display screen (not shown).
In the conventional projection display 1, the dichroic beam splitter prism 14 and the polarization beam splitter prism 13 cooperate with the first and second light polarization selectors 11, 12 to separate the white input light beam 10 into the three color components 101, 102, 103 that are modulated by the three light modulators 15, 16, 17. However, in view of current manufacturing constraints, the polarization beam splitter 13 does not permit a very high transmission for P-polarized light. Thus, when the P-polarized third color component 103 is received by the polarization beam splitter prism 13, a small portion of the P-polarized third color component 103 will be reflected by the polarization beam splitter prism 13 to pass through the second side thereof, i.e. toward the dichroic beam splitter prism 14, thus resulting in a light leakage component 103xe2x80x2. This light leakage component 103xe2x80x2 will then be provided by the dichroic beam splitter prism 14 to the first or second light modulator 15, 16. When the first or second light modulator 15, 16 is inactive, the light leakage component 103xe2x80x2 will be reflected back to the dichroic beam splitter prism 14, and pass through the polarization beam splitter prism 13, the second light polarization selector 12, and the polarizer 18 to reach the projection lens 19, thereby resulting in a shift in the gray scale coordinate of the projected image and in a reduction in the image contrast to adversely affect the output quality of the projection display 1.
Therefore, the main object of the present invention is to provide a projection display that utilizes reflective light modulators and that is capable of overcoming the aforesaid light leakage drawback of the prior art to enhance both contrast and output image quality.
According to one aspect of the present invention, a projection display is adapted to process an input light beam that includes a first color component, a second color component and a third color component, and comprises:
a polarization beam splitter prism having a first side adapted to receive the input light beam, a second side, a third side opposite to the first side, and a fourth side opposite to the second side, the polarization beam splitter prism being adapted to separate the input light beam into the first and second color components, which pass through the second side thereof, and the third color component, a large portion of which passes through the third side thereof, the polarization beam splitter prism further allowing a small portion of the third color component, which serves as a light leakage component, to pass through the second side thereof;
a color synthesizing prism disposed adjacent to the second side of the polarization beam splitter prism, and adapted to separate the first and second color components and the light leakage component from the polarization beam splitter prism so as to travel in three different directions, respectively;
reflective first and second light modulators disposed adjacent to the color synthesizing prism so as to receive the first and second color components respectively therefrom, the first and second light modulators modulating the respective one of the first and second color components and changing polarization state of the respective one of the first and second color components when activated, the first and second light modulators reflecting modulated first and second color components back to the color synthesizing prism; and
a reflective third light modulator disposed adjacent to the third side of the polarization beam splitter prism so as to receive the third color component therefrom, the third light modulator modulating the third color component and changing polarization state of the third color component when activated, the third light modulator reflecting a modulated third color component back to the polarization beam splitter prism.
According to another aspect of the present invention, a projection display is adapted to process an input light beam that includes a first color component, a second color component and a third color component, and comprises:
a polarization beam splitter prism having a first side adapted to receive the input light beam, a second side, a third side opposite to the first side, and a fourth side opposite to the second side, the polarization beam splitter prism being adapted to separate the input light beam into the first and second color components, which pass through the second side thereof, and the third color component, a large portion of which passes through the third side thereof, the polarization beam splitter prism further allowing a small portion of the third color component, which serves as a light leakage component, to pass through the second side thereof;
a color splitter prism set disposed adjacent to the second side of the polarization beam splitter prism, and adapted to separate the first and second color components and the light leakage component from the polarization beam splitter prism so as to travel in three different directions, respectively;
reflective first and second light modulators disposed adjacent to the color splitter prism set so as to receive the first and second color components respectively therefrom, the first and second light modulators modulating the respective one of the first and second color components and changing polarization state of the respective one of the first and second color components when activated, the first and second light modulators reflecting modulated first and second color components back to the color splitter prism set; and
a reflective third light modulator disposed adjacent to the third side of the polarization beam splitter prism so as to receive the third color component therefrom, the third light modulator modulating the third color component and changing polarization state of the third color component when activated, the third light modulator reflecting a modulated third color component back to the polarization beam splitter prism.